Axial gap rotating-electric machines include a two-rotor one-stator axial gap rotating-electric machine having a structure including a pair of disk-shaped rotors arranged in the direction of the rotating shaft of the rotating-electric machine so as to face each other, and a stator interposed between the pair of rotors with a predetermined gap therebetween. The rotor includes a rotor core and one or a plurality of magnets arranged in the circumferential direction, and the stator includes a plurality of stator cores arranged in the circumferential direction and coils wound around the stator cores. The axial gap rotating-electric machine in this configuration is described for example in JP-A-2005-269778 as well.
In contrast, when the stator is held by a mold resin, a problem of electrical corrosion of the bearing arises. In other words, since the stator core is electrically insulated by the mold resin and is at a floating potential, a voltage is generated between the stator and the rotor due to the electrostatic capacity between the rotor and the stator. When this voltage is higher than the discharge starting voltage of an oil film of the bearing, electric discharge occurs in the bearing, and hence the service life of the bearing is shortened. As a countermeasure of the electrical corrosion of the bearing, a method of grounding the stator core is known (JP-A-2009-118628, for example).